Ultrasonic echoscopy provides information about an examined object which may be displayed in the form of an ultrasonic echogram. Such an echogram consists of a display of acoustic impedance discontinuities or reflecting surfaces in the object. It is obtained by directing a short pulse of ultrasonic energy, typically in the 1-30 MHz frequency range, into the examined object where any acoustic impedance discontinuities in the object reflect and return some of the energy in the form of an echo. This echo is received, converted into an electric signal and displayed as an echogram on a cathode ray oscilloscope, a film, a chart or the like.
The echogram may constitute either a one dimensional or a two dimensional representation and in both cases the information is contained in the position and magnitude of the echo displayed. In a one dimensional display, the position along a base line is used to indicate the distance to the reflecting surface whilst the magnitude of the echo is displayed for example as a deflection of the base line "A mode" or as an intensity change "B mode". In a two dimensional display, the position along a base line is used to indicate the distance to the reflecting surface as in a one dimensional display, and the direction of the base line is used to represent the direction of propagation of the acoustic energy. The two dimensional display is obtained by changing this direction of propagation of the acoustic energy and by instituting a similar but not necessarily identical movement of the base line of the display. The magnitude of the echo is displayed as for a one dimensional display, for example, as a deflection of the base line or as an intensity change.
The technique of ultrasonic echoscopy is used in medical diagnosis to obtain information about the anatomy of patients. This application of echoscopy is now well known. It has been described, for example, by D. E. Robinson in Proceedings of the Institution of Radio and Electronics Engineers Australia, Vol. 31, No. 11, pages 385-392, November 1970, in his paper entitled "The Application of Ultrasound in Medical Diagnosis". As pointed out in that article, ultrasonic echoscopy may be used to produce displays resembling anatomical cross-sections which have proved clinically useful when the desired information concerns physical dimensions, shapes of organs or structures or the like. Ultrasonic echography has proved of particular value as a diagnostic aid in the abdomen and pregnant uterus, eye, breast, brain, lung, kidney, liver and heart, these being areas of soft tissue with little bone and air.
In general, ultrasonic echoscopy is considered to complement other techniques to provide a more complete picture of the patient's condition. However, particularly in pregnancies, ultrasonic echoscopy may be useful in place of X-rays where the latter may not give sufficient information or may be dangerous.
In medical use, a pulse of ultrasonic energy is transmitted into a patient in a known direction and echoes are received from reflecting surfaces within the body. The time delay between a transmitted pulse and the received echo depends on the distance from the transmitter to the reflecting surface and the distance information so obtained may be displayed in a suitable way for interpretation and clinical use as a one-dimensional range reading or as a two-dimensional cross-section as previously described.
In many ultrasonic B mode investigations it is an advantage to scan quickly over the desired area. Quick scanning may be achieved either by mechanical means such as by linearly translating the transducer over the desired length or by oscillating the transducer over the desired angle, the speed of movement being determined by considerations such as the desired line density of the ultrasonic information. Alternatively linear and oscillatory scanning may be achieved by electronic means such as may be obtained with a switched linear array transducer or a sectoring phased array transducer.